border-1px($color)
  position relative
  &:after
    display block
    position absolute
    left: 0
    bottom: 0
    width: 100%
    border-top 1px solid $color
    content ' '

border-none()
  &:after
    display none

bg-image($url)
  background-image url($url + '@2x.png')
  @media (-webkit-min-device-pixel-ratio: 3),(min-device-pixel-ratio: 3)
    background-image url($url + '@3x.png')
